Cylinder deactivation (also called Displacement on Demand or DOD™), generally involves deactivating the intake and exhaust valves of up to half of the cylinders of a vehicle engine. Simultaneously, fuel flow to those cylinders is cut off, at the same time increasing air and fuel supplied to the remaining engine cylinders, which continue to operate and provide power for driving the vehicle. During the changeover, a torque bump or sag may be noticeable to the vehicle operator under at least certain conditions of operation of the engine.
In the development of automotive engines, DOD is of current interest for providing engine operation with higher efficiency during highway cruising and at lower speeds and loads. However, it is desired to provide smooth transitions between standard (STD) full cylinder operation and DOD (cylinder deactivation) operation, which will make the changeover essentially unnoticeable to the vehicle operator. In addition, it is desired to provide an increase in engine torque output during cylinder deactivation operation on less then all the engine cylinders in order to permit continued DOD operation when the vehicle operator calls for a moderate torque increase, or operation at a higher speed within the capabilities of the engine.